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In semiconductor fabrication processes, wafers are transferred between stations, such as storage, queuing, processing and other work stations. In typical automated wafer handling processes, a wafer is first picked up by a robotic arm for transfer from one station to another station. Next, the wafer is placed on an aligner for aligning and centering the wafer to a desired position using a notch or flat located on the wafer""s edge. Once properly aligned, the wafer is then placed in the desired station for processing. After the processing is completed at the desired station, the wafer may then be picked up and placed again at another station.
Each time that the wafer is picked up, placed, and aligned, contact is made with either the edge or the back side of the wafer and particles are generated. For instance, in a single wafer process cycle, the wafer may be contacted as many as twelve times when using a three-axis aligner or at least eight times when a single axis aligner is used.
In addition, the alignment process requires a dedicated aligning device and a separate step in the wafer process cycle. The dedicated aligning device often creates a bottleneck that limits the wafer throughput in the system and also introduces additional handling that generates particles. Adding aligners to the system may help to slightly increase this throughput problem but creates an undesirable increase in the cost, complexity and generation of particles to the wafer handling system. Accordingly, a system is desired for enhancing the wafer handling process by reducing the generation of particles and wafer damage so that the wafer yield is increased. Also, it is desired to increase the wafer throughput by performing the alignment process in parallel with moving the wafer.
The present invention is directed to a system for locating and orienting substrates, such as semiconductor wafers, during the pick up and transfer steps in an automated substrate handling process. In a semiconductor fabrication process, the system is able to reduce the generation of particles from and the contamination of semiconductor wafers. As a result, the wafer yield and throughput of the fabrication process are increased.
More particularly, the system includes a robotic arm for moving a wafer from one station to another station. An end-effector is connected to an end of the robotic arm for handling the wafer. The end-effector may include a mechanism for gripping the wafer, a mechanism, such as a motor, for moving the wafer gripping mechanism, and at least one sensory system for sensing the location and orientation of the wafer. A control processor operatively connected to the robotic arm and the end-effector calculates the location of the center and a notch or flat of the wafer based on data from the at least one sensory system. The control processor generates a signal to move the wafer gripping mechanism so that the wafer is centered on the end-effector when picked by the end-effector and is oriented at a predetermined position on the end-effector while the robotic arm is moving to another station. After the wafer is picked up by the end-effector, the control processor can refine the calculation of the center of the wafer and adjust the wafer""s orientation before being dropped off at the next station.
Other aspects, features and advantages of the present invention are disclosed in the detailed description that follows.